1. Field of the Invention
The present invention relates to an object gripping apparatus, a control method for the object gripping apparatus, and a storage medium. In particular, the present invention relates to an object gripping apparatus that captures an image of components (workpieces) piled up in bulk (the state where a plurality of components are randomly placed) using a camera and the like, estimates the position and orientation of each workpiece from the captured image, and grips each workpiece, to a control method for the object gripping apparatus, and to a storage medium.
2. Description of the Related Art
In order to pick up a target object (target workpiece) from among workpieces piled up in bulk by controlling a robot hand, an image of the state of the workpieces piled up in bulk is captured first using a camera and the like, and then the position and orientation of a workpiece to be gripped by the robot hand are estimated using some sort of method. Thereafter, it is necessary to calculate a path along which the robot hand operates to grip the workpiece based on the estimated position and orientation of the workpiece.
In Japanese Patent Laid-Open No. 5-127718, a plurality of trajectory templates showing estimated head-trajectories of a robot hand are registered in advance, and the interference between the robot hand and obstacles is inspected based on the plurality of trajectory templates. Head-trajectories of the robot hand are generated based on trajectory templates for which it is determined that the interference does not occur as a result of the inspection.
In Japanese Patent Laid-Open No. 10-128686, a position/orientation candidate that an object could take is obtained based on an image or a range image, and based on the obtained position/orientation candidate, an environmental model is generated by dividing a space into an object space and other spaces. Based on the generated environmental model, an operation path of a robot hand for picking up a target object is generated.
In Japanese Patent Laid-Open No. 2006-175532, a plurality of different path patterns are stored in a path pattern storage unit as the approaching and leaving paths of a robot hand. Next, based on a workpiece position detected by a visual sensor, one of the plurality of path patterns stored in the path pattern storage unit is selected. The selected path pattern is modified so that the target position of the robot hand is coincident with the actual workpiece position. The modified path pattern is defined as revised approaching and leaving paths and the robot hand is moved along the revised approaching and leaving paths.
In Japanese Patent Laid-Open No. 1-183395, in order to reduce the cycle time of workpiece pickup, a shield unit is provided to a robot hand so as to allow capturing an image for pickup of the next workpiece while the robot hand is attempting to grip a workpiece. Normally, when an image is captured while the robot hand is attempting to grip a workpiece, the robot hand is captured in the image as well. This obstructs subsequent image processing. In view of this, the shield unit is provided to make easy the separation between a shielded region and an unshielded region in the image and to enable subsequent image processing.
As mentioned above, in order for a robot hand to pick up workpieces piled up in bulk in sequence, it is necessary to calculate paths along which the robot hand operates to grip the workpieces. In terms of operational efficiency, it is desired to calculate paths that enable the operation to finish in a short period of time.
However, the method described in Japanese Patent Laid-Open No. 5-127718 selects paths based on whether or not the interference with obstacles has occurred, and therefore gives no regard to selection of paths that reduce the operating time.
The method described in Japanese Patent Laid-Open No. 10-128686 generates an operation path so as to guarantee a space that a robot hand can enter between a target object to be gripped and other objects. Therefore, this method does not give any regard to selection of paths that reduce the operating time, either.
The method described in Japanese Patent Laid-Open No. 2006-175532 aims to reduce the operating time by preparing, in advance, path patterns that reduce ineffectual operations of a robot hand while avoiding the interference with other objects in accordance with the actual positions of workpieces. That is to say, the method described in Japanese Patent Laid-Open No. 2006-175532 selects path patterns based on the positions of workpieces, but not based on the length of the operating time. Furthermore, this method gives no regard to a reduction in the operating time for the case where the robot hand picks up workpieces piled up in bulk in sequence.
The method described in Japanese Patent Laid-Open No. 1-183395 reduces the cycle time of workpiece pickup by providing a shield unit to a robot hand so as to allow capturing an image for pickup of the next workpiece while the robot hand is attempting to grip a workpiece. However, this method cannot obtain an image of workpieces included in a shielded region, and therefore restricts selection of a target workpiece in the course of picking up workpieces in sequence.
The following problem exists in reducing the operating time required to pick up workpieces piled up in bulk in sequence.
In general, in order to pick up workpieces piled up in bulk in sequence, a workpiece to be picked up (target workpiece) is determined by capturing an image of the state of the workpieces piled up in bulk using a camera or the like and estimating the position and orientation of each workpiece using the captured image. Then, the robot hand is controlled to grip the target workpiece and convey the target workpiece to a designated deposit position. This procedure is repeated in sequence.
To accelerate the above operation, after the robot hand grips the target workpiece, it is necessary to capture an image for the next target workpiece as soon as possible. However, if the image is captured the moment the robot hand grips the target workpiece, the captured image includes the robot hand. This obstructs estimation of the positions and orientations of workpieces. Even if the image is captured during conveyance of the gripped target workpiece, there may be cases where the captured image includes the robot hand. This obstructs estimation of the positions and orientations of workpieces as well.
That is to say, in order to reduce the operating time required to pick up workpieces in sequence, it is necessary to operate a robot hand so that a camera can capture an image as soon as possible after a target workpiece is gripped. However, conventionally, this operation has not been taken into consideration.